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Touch and Pain #8
Terms in this set (58)
Touch receptors may be
-Simple bare neuron ending
Simple bare neuron ending
Warm, cold and pain
• Eg. modified dendrites (Merkel disks)
• elaborated neuron ending
Stimulation opens what kind of channels to trigger an action potential?
they are activated by physical force.
Stretching or displacement of the skin
opens channels to activate them.
When activated (mechanoreceptors)
they send APs up the axon toward the spinal cord.
The sensory neuron cell body is located in the
DRG *These are afferent fibers - they go toward the CNS.
Meissner's corpuscle and Merkel disks:
Fine detail, and Movement (if you stroke an
object to explore its shape)
Pacinian corpuscle and Ruffini endings:
Stretch, Perception of the shape of a grasped object.
A group of sensory neurons that converge on the same neuron in the spinal cord form a
receptive field * Receptive fields overlap to some extent. This lets us feel touch over our entire bodies.
The more closely‐packed these fields are
the more sensitive the area is to touch stimuli.
Do men or women have more detail to touch?
receptors that respond to light touch (i.e., gentle stroking of the skin) *Men and women generally have the same number of Merkel disks, but women tend to have smaller fingers.
Information from touch receptors in the head
enters the CNS through the cranial nerves.
Information from receptors below the head
enters the spinal cord and travel through the 31 spinal nerves to the brain.
Each spinal nerve has
a sensory component and a motor component and connects to a limited area of the body.
skin area connected to or innervated by a single sensory spinal nerve (they overlap)
Sensory information entering the spinal cord travel
in well‐defined and distinct pathways. (Example: touch pathway is distinct from pain pathway)
send impulses to different areas of the somatosensory cortex
is located in the parietal lobe.
Different sub areas of the somatosensory cortex respond to
different areas of the body.
Damage to the somatosensory cortex can result in the
impairment of body perceptions
The homunculus corresponds to the areas of
greatest innervation in humans.
Rats investigate with their
nose & mouth more than anything else.
Each whisker has a large field of cortical representation.
These are called whisker barrels.
Pain is the experience evoked by
a harmful stimulus, directs our attention, and holds it.
Pain sensation begins with the least specialized of all receptors
bare nerve endings
a chemical found in hot pepper; stimulates these receptors
Axons carrying pain info have little or no myelin
impulses travel slowly. *However, brain processes pain information rapidly and motor responses are fast.
Mild pain triggers the release of
glutamate in the spinal cord and stronger pain triggers the release of glutamate and substance P
results in the increased intensity of pain
Pain receptors: Mechanical
pinching and cutting
Pain receptors: Thermal
hot and cold
Pain receptors: Polymodal
all mechanical and thermal plus chemicals released when tissue is injured
Nociceptors respond to AND release chemical stimuli
(the basis of inflammation)
Pain is Pure Perception:
The stimulus is tissue damage
Pain pathways cross to a tract ascending the contralateral side of the spinal cord. Pain‐sensitive cells in the spinal cord relay information to several areas of the brain.
responds to painful stimuli, memories of pain, and signals that warn of impending pain
Central nuclei of the thalamus, amygdala, hippocampus, prefrontal cortex and cingulate cortex are
associated with emotional associations.
Opioid mechanisms are systems that are sensitive to opioid drugs and similar chemicals
Activating opiate receptors blocks the release of substance P in the spinal cord and in the periaqueductal gray area of the midbrain
Cannabinoids are chemicals related to marijuana that also block certain kinds of pain
Act mainly in the periphery of the body
Capsaicin dumps substance P so you have to remake it OR
can damage the actual pain receptor
the spinal cord areas that receive messages from pain receptors also receive input from touch receptors and from axons descending from the brain
- These other areas that provide input can close the "gates" and decrease pain perception
- Non‐pain stimuli around it can modify the intensity of the pain
Pain signals ascend the pain pathway and reach conscious awareness in the thalamus & cortex.
"Descending" pathways can keep the CNS from receiving pain signals.
they close the gate to pain.
The CNS activates neurons that release endorphins.
- This blocks the release of substance P.
- This keeps pain signals* from getting in.
Descending Brainstem fiber
A placebo is a drug or other procedure with
no pharmacological effect.
- Decreases pain perception by decreasing the brain's emotional response to pain perception, not the sensation itself
- Decreases response in cingulate cortex but not in the somatosensory cortex
Mechanisms of the body to increase sensitivity to pain include:
• Damaged or inflamed tissue releases histamine, nerve growth factor, and other chemicals that increase the responses of nearby pain receptors
• Non‐steriodal anti‐ inflamatory drugs (ibuprofen) decrease
chemicals that pester pain receptors
Certain receptors become potentiated after an
intense barrage of painful stimuli
Leads to increased sensitivity or chronic pain later
Emotional pain resembles physical pain in
- Increased activity in the cingulate cortex when someone felt left out of an activity
- People taking acetaminophen (Tylenol) reported less incidences of hurt feelings and social pain
Itch is not pain!!
The release of histamines by the skin produce itching sensations
- Activates a distinct pathway in the spinal cord to the brain
- Impulses travel slowly along this pathway (half a meter per second)
Pain and itch have an inhibitory relationship
Opiates increase itch while antihistamines decrease itch
• Poorly understood
• Maybe social communication
• The laughing is not normal laughter in that it doesn't predict subsequent laughter
• Most people do not like to be tickled
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